The present invention relates to a beam scanning optical apparatus for creating an image through beam scanning.
Heretofore, a beam scanning optical apparatus has been used as an image writing means in an electrophotographing process, and has been incorporated in a laser printer as an output unit of a computer or a facsimile machine, a laser facsimile and the like. Recently, there has been raised a demand for a high speed color laser printer, and accordingly, there has been highly interested in a tandem type beam scanning optical apparatus for this high speed color laser printer.
Next, a beam scanning optical apparatus incorporated in conventional tandem type color image forming apparatus will be explained with reference to FIGS. 6 and 7.
FIG. 6 is a view for explaining a cooler image forming apparatus incorporating a conventional beam scanning apparatus, and FIG. 7 is a plan view illustrating the beam scanning optical apparatus shown in FIG. 6.
As shown in FIG. 6, four imaging stations are located in the cooler image forming apparatus, respectively comprising photosensitive drums (photosensitive media) 10a, 10b, 10c, 10d serving as image bearing media, and further, there are provided around the respective photosensitive drums 10a, 10b, 10c, 10d, electrifiers 11a, 11b, 11c, 11d for uniformly electrifying the outer surfaces of the photosensitive drums 10a, 10b, 10c, 10d, development parts 12a, 12b, 12c, 12d for developing latent images, cleaning members 15a, 15b, 15c, 15d for removing residual toner, erasers 16a, 16b, 16c, 16d for initializing the surface potential of the photosensitive drums 10a, 10b, 10c, 10d, optical units 8a, 8b, 8c, 8d serving as beam scanning optical apparatuses for irradiating light beams which correspond to image data, onto the photosensitive drums 10a, 10b, 10c, 10d. 
In this arrangement, the image stations create an yellow image, a magenta image, a cyan image and a black image, respectively, and the optical units 8a, 8b, 8c, 8d emit beams 9a, 9b, 9c, 9d as scanning beams, respectively corresponding to the black image, the yellow image, the magenta image and the cyan image. Further, these beams 9a, 9b, 9c, 9d form predetermined electrostatic latent images in surfaces 7a, 7b, 7c, 7d to be scanned on the photosensitive drums 10a, 10b, 10c, 10d, respectively.
As shown in FIG. 7, the optical units 8a, 8b, 8c, 8d respectively incorporate, beam emitters 1a, 1b, 1c, 1d, and deflectors 3a, 3b, 3c, 3d for deflecting beams emitted from the beam emitters 1a, 1b, 1c, 1d, scanning lenses 4a, 4b, 4c, 4d for focussing the deflected beams on the surfaces 7a, 7b, 7c, 7d to be scanned, mirrors 5a, 5b, 5c, 5d for leading the beams onto the surfaces 7a, 7b, 7c, 7d to be scanned, and synchronous detectors 6a, 6b, 6c, 6d for detecting synchronization among the beams.
An intermediate transfer belt (intermediate transfer medium) 13 in the form of an endless belt is laid below the photosensitive drums 10a, 10b, 10c, 10d, running through the respective imaging stations, and being supported by two rollers. The intermediate transfer belt 13 is turned around in a direction indicated by the arrow.
First transfer units 14a, 14b, 14c, 14d for transferring toner images created on the respective photosensitive drums 10a, 10b, 10c, 10d onto the intermediate transfer belt 13 are provided in the vicinity of the respective photosensitive drums 10a, 10b, 10c, 10d, the intermediate transfer medium being interposed therebetween.
It is noted that the toner images on the intermediate transfer belt 13 are transferred on to a sheet 17 fed from a stack of sheets stored in a paper feed cassette, by means of a second transfer unit 18, and then, the sheet is discharged onto a discharge tray (which is not shown) by way of a fixing unit 19.
In the cooler image forming apparatus having the above-mentioned structure, when a predetermined color image output signal is received, the rotation of the respective photosensitive drums 10a, 10b, 10c, 10d and the intermediate transfer belt 13 is started. Further, the respective photosensitive drums 10a, 10b, 10c, 10d are uniformly electrified by the electrifiers 11a, 11b, 11c 11d at predetermined potentials.
Meanwhile, in the respective optical units 8a, 8b, 8c, 8d, the deflectors 3a, 3b, 3c, 3d deflect the beams from the beam emitters 1a, 1b, 1c, 1d. The image zones on the photosensitive drums 10a, 10b, 10c, 10d are scanned with the thus deflected beams, respectively, by means of the mirrors 5a, 5b, 5c, 5d so as to carry out exposure. Before scanning the image zones of the photosensitive drums 10a, 10b, 10c, 10d, the beams are synchronized with one another by means of the synchronous detectors 6a, 6b, 6c, 6d, and then, the beams are irradiated, corresponding to image data, with a predetermined timing.
After the exposure by the beams, the electrified potentials on the outer surfaces of the photosensitive drums 10a, 10b, 10c, 10d are lowered so that electric latent images corresponding to the image data are created thereon. Thus, the optical units 8a, 8b, 8c, 8d create the latent images on the photosensitive drums 10a, 10b, 10c, 10d for the respective colors in response to the image data corresponding respectively to black, yellow, magenta and cyan.
The electric latent images created on the photosensitive drums 10a, 10b, 10c, 10d are developed with respective color toners by means of the developing parts 12a, 12b, 12c, 12d so as to be turned into color toner images. These toner images are transferred onto the intermediate transfer belt 13 by the first transfer units 14a, 14b, 14c, 14d so that the toner images having black, yellow, magenta and cyan are superposed with one another on the intermediate transfer belt 13.
After the superposition of the four cooler toner images is completed on the intermediate transfer belt 13, these four cooler images are transferred in a batch onto the sheet 17 fed from the paper feed cassette, by means of the second transfer unit 18, and are then heated for fixing so that a full cooler image can be obtained on the sheet 17.
It is noted that residual toner on the respective photosensitive drums 10a, 10b, 10c, 10d is removed by the cleaning members 15a, 15b, 15c, 15d after completion of the transfer of the images, and then, the respective photosensitive drums 10a, 10b, 10c, 10d are electrically initialized by the erasers 16a, 16b, 16c, 16d in preparation for the successive image formation. Thus, the printing operation is completed.
Thus, the images having back, yellow, magenta and cyan can be formed in parallel with one another, and accordingly, a beam scanning optical apparatus which can cope with high speed color printing can be obtained.
However, in the conventional beam scanning optical apparatus as mentioned above, since the four optical units are arranged, not only the body of the image forming apparatus becomes large-sized, but also the weight thereof becomes higher, resulting in inclusion of a high cost.
Accordingly, an object of the present invention is to provide a compact beam scanning optical apparatus.
To the end, according to the present invention, there is provided a beam scanning optical apparatus comprising a first beam optical system composed of a plurality of optical blocks, in which beams emitted from beam emitters are deflected by deflectors and are then led to scanning lenses by means of mirrors so as to be focused on a surface to be scanned, and a second optical systems composed of a plurality of optical blocks, in which the beams emitted from the beam emitters are deflected by deflectors, and then led to scanning lens by means of mirrors so as to be focused on the surface to be scanned, and which is stacked with the first optical system one upon another, wherein the advancing directions of the beams in the first and second optical systems are reverse to each other from the deflectors to the scanning lenses, and the beam in the second optical system passes between optical elements in the first optical system in order to scan the surface to be scanned.
With this arrangement, the length of the beam scanning optical apparatus can greatly be reduced in comparison with an arrangement in which optical blocks are juxtaposed with one another, thereby it can have a compact size.
According to a first aspect of the present invention, there is provided a beam scanning optical apparatus including a first optical system composed of a plurality of optical blocks for deflecting beams emitted from beam emitters with the use of defectors, and thereafter, leading the beams to scanning lenses through the intermediary of mirrors so as to be focused onto a surface to be scanned, and a second optical system composed of a plurality of optical blocks for deflecting beams from beam emitters with the use of deflectors, and thereafter leading the beams to the scanning lenses so as to be focused onto a surface to be scanned, and stacked with the first optical system one upon another, the advancing directions of the beams in the first and second optical systems being reverse to each other from the deflectors and the scanning lenses, and the beams in the second optical system passing through between optical elements in the first optical system and then scanning a surface to be scanned. With this arrangement, there can be provided such a beam scanning optical system that its length can be greatly reduced, thereby it is possible to provide such an advantage that a beam scanning optical system can have a compact size in comparison with a conventional arrangement in which optical blocks are juxtaposed with one another
According to a second aspect of the present invention, there is provided, in addition to the arrangement of the first aspect of the present invention, there is provided a beam scanning optical system in which the optical blocks are separated into a predetermined number of groups. With this arrangement, there can be offered such an advantage that the cost and the molding terms of a housing which constitutes each of the optical blocks, can be reduced.
According to a third aspect of the present invention, in addition to the arrangements of the first and second aspects of the present invention, there is provided a beam scanning optical apparatus in which the scanning lenses in the optical blocks constituting the first optical system have surfaces one side, serving as attachment surfaces, and the scanning lenses in the optical blocks constituting the second optical system, have surfaces on a side in opposite to the former side, serving as mounting surfaces. With this arrangement, the difference in scanning curvature can be relaxed, and accordingly, there can be offered such an advantage that color can be restrained from oozing when color toner images are superposed with one another, and misalignment of colors can be reduced.
According to a fourth aspect of the present invention, there is provided a beam scanning optical apparatus, in addition to the first to third aspects of the present invention, in which the beam emitters emit light beams laterally of the optical axes of the canning lenses, thereby it is possible to offer such an advantage that the workability and the reliability of electrical connection between the beam scanning optical system and an image forming apparatus.